<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>循环大练习04</title>
</head>

<body>
    <script>
        let num = +prompt('请输入一个整数')
        let he = 0
        for (let i = 1; i < num; i++) {
            he += i
        }
        console.log(he)
        alert(he)
    </script>
</body>

</html>